Enrico Fermi

Designer of First Nuclear Reactor

Born in Rome on September 29, 1901, and educated there, Fermi received his doctorate from the University of Pisa when he was only 21. In 1926 he became a professor of physics at the University of Rome. That same year he developed the mathematics underlying the behavior of electrons, verifying what is called the “exclusion principle,” which says that no two electrons in an atom can exist in identical states. That is, something must be different about each electron—the orbital in which it lies around the nucleus, the shape of the cloud that it forms, or the direction of its spin.

In the early 1930s, exciting discoveries drew Fermi into experimental physics. In 1932 JAMES CHADWICK discovered that atomic nuclei contain neutral particles called neutrons, and two years later Irene Curie (daughter of scientists Pierre and MARIE CURIE) and her husband Frédéric Joliot found that they could produce new, radioactive isotopes by bombarding stable, naturally occurring atoms with alpha particles—positively charged particles discharged from radioactive material. Fermi realized that neutrons, with no charge, could penetrate atoms more easily than positively charged alpha particles and might be more effective in promoting nuclear reactions. His team of young physicists attacked the elements of the periodic table with zeal, producing scores of radioactive isotopes that had never been seen before. When Fermi bombarded uranium, the heaviest known element, he had surprising results. He and his team thought they were seeing a new, heavier element, but in 1939 LISE MEITNER and OTTO HAHN explained the results as the fission or splitting of uranium, leading to the development of nuclear weapons.

Fermi and his wife Laura escaped from the Fascist government of Italy in 1938, the year he received the Nobel Prize for Physics for his work on radioactivity and neutron bombardment. He came to the University of Chicago in 1939 and three years later joined the Manhattan Project, sponsored by the U.S. government to build the first nuclear weapons. On December 2, 1942, a team under his direction pulled the control rods from the first experimental nuclear reactor and released nuclear energy as planned, demonstrating for the first time that a sustainable, controlled series of fission reactions was possible.

Element number 100 is fermium, named for him, and an annual Enrico Fermi award is given in the United States for advances in nuclear theory and peaceful uses of nuclear energy. He died of cancer in Chicago on November 28, 1954.

Enrico Fermi’s Legacy

Enrico Fermi made groundbreaking advances in nuclear theory and its application, innovations that profoundly affected science and the world.

Fermi’s theoretical work alone leaves a tremendous legacy; it has come to explain fundamental phenomena in physics and chemistry. Particles that make up the material universe—protons, neutrons, electrons, and the quarks that make up protons and neutrons—have the value of a property called spin, which makes them subject to the rules that Fermi described. All of those particles are called fermions. In any bound system, such as an atom, no two fermions can ever be identical. This explains the organization of electrons within atoms, the patterns of chemical behavior, the durability of matter, and matter’s ability to take up space.

Fermi’s leadership on the Manhattan Project was invaluable; he was described as the most versatile scientist on the project and was respected by all of the scientists working on it. While his work on the nuclear reactor in 1942 was instrumental in the creation of the atomic bombs dropped on Japan and ultimately led to the development of the United States’ nuclear arsenal, he urged caution. With other colleagues, including J. ROBERT OPPENHEIMER and ALBERT EINSTEIN he helped to form the moral imperative against further development of nuclear weapons, in particular the more powerful hydrogen bomb, following the first demonstrations of their destructive capacity

The technique Fermi developed for creating and analyzing nuclear isotopes is used today in neutron activation analysts, one of the most precise analytical methods ever developed. A sample to be analyzed is exposed to a powerful beam of neutrons, making many of its component atoms radioactive. Each emits radiation characteristic of that new isotope, giving technicians a unique fingerprint of that element’s presence. Chemical detection methods always require trillions of atoms or molecules to make a detectable reaction, but equipment to measure radiation detects the decay of single atoms, making it possible to determine the tiniest quantities of materials. A sample of Napoleon’s hair was analyzed with this method, revealing chemically undetectable traces of arsenic, suggesting that he may have been poisoned.